Packet networks, such as the Internet, have evolved to a point where voice communications are capable of being supported with quality rivaling that of calls supported by the traditional public switched telephone network (PSTN). Since packet communications are inherently more efficient than the circuit-switched communications of the PSTN and allow voice calls to be associated with any number of other media sessions to provide advanced services, traditional telephony services are now supported over packet-based networks.
Two of the challenges with providing traditional telephony services over packet networks are meeting the expectations of the public and fulfilling legal requirements associated with telephony services. The public demands a telephone experience emulating that of the PSTN. In essence, the public needs a packet telephony interface to behave like a traditional telephony interface, which provides dial tones, dialed digit tones, ringing signals, busy signals, call waiting alerts, and the like. Service providers for packet telephony services are building terminals and configuring network devices to emulate traditional telephony services.
From a legal perspective, there are various requirements for telephony services. These requirements need to be fulfilled for packet telephony services. Of particular importance are the requirements for handling emergency services calls, such as those invoked when dialing 911 in the United States. In general, emergency services calls must be given priority and be immediately connected to an emergency services call center. Once an emergency services call is connected, a forced hold service may be invoked to assist in maintaining a connection with the caller's telephone terminal, even if the telephone terminal goes onhook or otherwise holds the call session. If the telephone terminal goes onhook, the connection is maintained to allow the caller to quickly reconnect to emergency services by simply taking the telephone terminal offhook. Alternatively, the emergency services operator can initiate a ringback function to cause the telephone terminal to ring, wherein the telephone terminal is reconnected to the maintained connection upon the telephone terminal going offhook. A full description of overall forced hold functionality is provided in ANSI T1.628A-2001: Network Hold, which is incorporated herein by reference.
Accordingly, there is a need for an efficient and reliable technique to provide a forced hold service in a packet network environment. Given the significant emergency services infrastructure already provided by the PSTN, there is a further need to take advantage of the PSTN's emergency services infrastructure when providing forced hold services in a packet network environment.